New UHV angle encoder for high resolution monochromators, a modern spare part for the Heidenhain UHV RON 905

There are a large number of soft X-ray grating monochromators for high-resolution synchrotron radiation experiments in operation worldwide. At BESSY II eighteen of the monochromators currently in use are equipped with Heidenhain UHV RON905 angle encoders. Those angle encoders have successfully been in operation for decades. Today, this type of encoder has become a legacy product and repairs are getting expensive. Therefore, we have developed a new angle encoder, a mechanically compatible drop-in replacement of the RON905. A mechanically fitting prototype, based on RENISHAW absolute encoders, was tested on a high precision angle drive test bench. Fourier analysis of the encoder data allowed us to determine the precision for different angle ranges and indicates a better precision for the new angle encoder. Furthermore, we will introduce an on-line, in-situ method using electron/absorption spectroscopy to improve system accuracy with plane grating monochromators in collimated light using the newly developed encoder.